Electrochemical cells in which lithium acts as an anode and sulfur dioxide acts as a depolarizer are becoming increasingly important as uses for these batteries are developed by the industry. The cells offer advantages of high energy and light weight, and much is being learned about these cells as efforts are made to increase the predictability and dependability of the cells employing lithium and sulfur dioxide.
Many patents disclose combinations of this type wherein lithium and sulfur dioxide are employed. One such patent, U.S. Pat. No. 3,567,515 discloses a system in which lithium is the anode, sulfur dioxide is the major cathode depolarizer and an electrolyte salt is dissolved in the sulfur dioxide, oftentimes along with a co-solvent. U.S. Pat. No. 3,578,500 discloses this same concept, along with the use of various soluble depolarizers acting with or instead of the sulfur dioxide, with the sulfur dioxide still performing the function of a solvent. So does U.S. Pat. No. 3,953,234.
As various cells are constructed to meet commercial objectives, using lithium and sulfur dioxide, various problems have developed requiring selection of components which are compatible with one another. Each of the above-referred to patents lists a substantial number of salts which may be dissolved in an equally substantial number of solvents, along with the sulfur dioxide.
One particular use for lithium sulfur dioxide electrochemical cells which has not yet achieved a significant commercial success is the reserve cell. These reserve cells, wherein a portion of the components making up the electrochemical reaction are segregated or remote from the remaining portion of the constituents, have a potential usefulness which is different from the active cell described in the above discussed patents. In an active cell, where all of the constituents of the electrochemical reaction are together, energy may be taken from the cell merely by applying a load. Substantial work has been done to completely understand all of the reactions which take place when lithium, sulfur dioxide, a salt, and possibly a co-solvent are present in one chamber. Conversely, when one or more of these constituents are not present in the system, such as in a reserve cell where one or more constituents are contained in a remote compartment, different reactions may take place between those constituents which are mixed together. Moreover, reactions between several constituents which are inhibited by the presence of a third constituent may be accelerated in the absence of that third constituent.
Reserve cells have achieved certain commercial successes employing various chemistries. One reserve cell system is disclosed in U.S. Pat. No. 3,743,545, in which an activation means is provided to transfer a quantity of electrolyte to the cell, thereby energizing the cell. Each set of constituents for the electrochemical cell described in this reference is compatible with those with which it is placed. Specifically, U.S. Pat. No. 3,743,545 deals with an ammonia battery system in which the ammonia and dissolved salts are maintained in a chamber remote from the electrochemical cell until operation of the cell is desired. Another useful reserve cell system is disclosed in U.S. Pat. No. 3,514,339.
It is an object of this invention to provide a cell in which both lithium and sulfur dioxide are employed in a manner known in the art, and in which sufficient constituents of the cell are separated from the remaining constituents so that no electrochemical reaction can take place until the constituents are all brought together.